Odds of El Niño visiting have gone up

The odds of an El Niño weather pattern arriving by this fall were raised Thursday, and that means the chances of a rainy winter in Southern California are going up.

The Climate Prediction Center in Maryland now says there’s a 65 percent chance an El Niño will develop by the October-December period. That’s up from a 50 percent chance listed in June.

El Niños occur when the sea-surface temperatures in the equatorial Pacific climb above normal for several months. The added warmth alters atmospheric weather patterns, usually shifting the average storm track away from the Pacific Northwest and more into California.

The pattern develops periodically and irregularly. It is not a guarantee of a wet winter in San Diego, but it is like loading the dice in favor of rainy weather.

El Niños have pluses and minuses. Some have caused flooding and coastal erosion in California, but they can also replenish depleted watersheds in the state and in the drought-stricken Southwest.

If El Niño develops early, it could also put a damper on the Atlantic hurricane season, reducing the odds of damaging hurricane landfalls this year. The CPC says the condition could develop as early as this summer.

But not all El Niños have predictable impacts. Some weaker El Niño episodes, when the sea-surface temperatures are only marginally above normal, can be overpowered by other global patterns. At this point, the emerging El Niño does not appear to be too powerful.

One thing El Niño almost always does is raise the average global temperature. If El Niño develops as expected, 2012, which has already been exceptionally warm across most of the U.S., will likely go down as the warmest year on record globally.